Shelton, the leading voice of the unsuccessful campaign against marriage equality, made the announcement with Bernardi in Toowoomba.

Lyle Shelton quits Australian Christian Lobby to enter politics

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It had been expected that Shelton would announce plans to stand in the next federal election but instead Bernardi announced Shelton would become the “spokesman for the party outside of the parliamentary ranks”.

Shelton told a crowd of Australian Conservatives supporters that, after a decade “fighting for truth and freedom” for the Christian lobby, he had decided that Canberra was “broken” and that the major political parties had “abandoned their virtues”.

He said the campaign for marriage equality had demonstrated “the lack of common sense and principles in Canberra”.

“Watching a Coalition government tear itself apart over whether or not marriage should be between something as basic as a man and a woman helped me to realise that Australia’s conservative political party had lost its way,” he said.

“The Coalition government’s inability or unwillingness to even provide basic protections for freedom of speech and freedom of religion quite frankly left me stunned.”

As head of the ACL, Shelton helped spearhead not only the No campaign but also the conservative push against the Safe Schools education program. In his speech on Sunday he complained that conservative politicians had “capitulated” and “handed over” social policy to the “green rainbow left”.

“As a result of their silence, elites are telling us we’re bigots if we don’t support teaching children their gender is fluid,” he said. “Elites label us deniers if we simply question anthropomorphic global warming [and] we just have to cop the high cost of electricity while governments shut down power stations.”

Since defecting from the Liberal party in February last year, Bernardi has lured two former Family First members in the South Australian upper house and one former Democratic Labor party member of the Victorian upper house to the Australian Conservatives.

The party is yet to win a seat in an election but conservative figures such as the former prime minister Tony Abbott have previously predicted Bernardi’s fledgling party would benefit from the unsuccessful campaign against same-sex marriage.

In an increasingly crowded field of often rightwing parties, the Australian Conservatives have tried to market themselves as a credible alternative.

Bernardi says his party “contains close to 20,000 formal members” and had received more than 20,000 individual donations in the past 12 months.

“Our goal is to not only win seats in the lower house but more importantly to hold and win seats in the Senate and upper houses of [state] parliaments,” he said. “If, as Australian Conservatives, we can garnish 10% of the vote in our respective states, we will win Senate seats in those states.

“If we can do that over successive elections we will be a force to be reckoned with. It means you cannot enact policies that lack common sense, that lack prudence for the future or the wisdom of considering what is important for our children.”